Communication systems, such as for earth-satellite communication, present a need for an extremely high-speed, reliable and difficult to intercept communication link. Known communication systems lose data due to signal fade or atmospheric turbulence. Optical links through the atmosphere using limited sized apertures are subject to short-term drop-outs due to atmospheric turbulence. At desirable transmission rates of up to approximately 10 gigabits per second (Gbps) even short drop-outs cause the loss of large volumes of data. For the 10 Gbps example, 50 million bits of data are lost in a 5 ms dropout. Dropout characteristics can also be asymmetrical, such that drop-out is worse for an uplink than for a downlink.
To help prevent data loss, standard forward error correction (FEC) coding techniques such as Reed-Solomon or Turbo codes or a concatenation of Reed-Solomon with Viterbi coding are employed. Reed-Solomon coding works by constructing a polynomial from the data symbols to be transmitted. The redundant data allows the reconstruction of the original polynomial even with transmission errors or drop-outs of data. Reed-Solomon and other known coding techniques work well to eliminate short bursts of drop-out data, but become ineffective when encountering large bursts of errors, such as a drop-out that involves an extremely large number of bits. For example, forward error correction (FEC) gain achieving a 10−10 bit error rate (BER) at the output with a 10−6 BER from the receiver, having a 5 ms drop-out in the exemplary 10 Gbps link, would require a 1.4 hour block length (50 trillion bits) for the BER within the block to be 10−6. Use of known block interleavers to achieve this spacing would result in an unacceptably high transport delay, making the link unusable.